The judge ruled that Mr Hunt lacked power after being told the changes would mean local people having "to travel a long, long way further to get access to vital services".

The Government is now asking the Court of Appeal to rule Mr Justice Silber went wrong in law.

The Health Secretary was attempting to deal with problems created by the financial collapse of neighbouring South London Healthcare NHS Trust, which went into administration after it started losing more than £1 million a week.

Quashing Mr Hunt's decision, the judge declared that he had breached provisions of the National Health Services Act 2006.

The ruling was a serious blow for Mr Hunt because the case involved the first legal testing of a new Government procedure for dealing with failing NHS organisations - referred to as the Unsustainable Providers Regime.

Under the new regime, Mr Hunt had appointed a Trust Special Administrator (TSA) to the "very badly performing" South London Healthcare Trust.

The judge said that last year the Trust reported a deficit of £65 million, "making it the most financially challenged Trust in the NHS". It is expected to run up an accumulated deficit of £196 million by 2017.

To help deal with the problem, the special administrator recommended measures including cuts at Lewisham Hospital. Mr Hunt told Parliament in January that A&E and maternity services at the hospital would be downgraded.

Mr Hunt assured MPs the changes would improve patient care in south London, saving up to 100 lives a year, but gave an undertaking not to implement them pending the legal challenge.

His appeal will be heard over two days by a panel of three judges - Lord Dyson, Master of the Rolls, sitting with Lord Justice Sullivan and Lord Justice Underhill.

Rosa Curling from law firm Leigh Day, who represented the Save Lewisham Hospital Campaign, said: "We remain confident that the Court of Appeal will uphold Mr Justice Silber's decision and we intend to request an urgent hearing so the ongoing uncertainty facing the hospital can be brought to an end as a matter of priority."

Tony O'Sullivan, from the Save Lewisham Hospital Campaign, said: "We are disappointed by the Secretary of State's decision to launch an appeal. However, we are confident that the strength of our case will be upheld at appeal.

"Our commitment to defend the excellent services provided by Lewisham hospital is unwavering."

A Department of Health spokeswoman said: "The proposed changes to Lewisham hospital are just one aspect of a package of measures which we believe are in the best long-term interests of patients and the public across south east London.

"South London Healthcare NHS Trust has been running at a loss of about £1 million a week - that's money that has to be diverted from frontline patient care.

"So of course we were disappointed by the High Court decision to block the changes - and we have now appealed this decision.

"We expect to continue with other elements of the process, including the dissolution of the South London Healthcare NHS Trust, planned for 1 October - although there are a number of steps to go before that can take place."